1. Technical Field
The present invention relates to a surface acoustic wave resonator and a surface acoustic wave filter using the same which are used in particular for cellular phones or the like.
2. Background Art
Conventionally, such surface acoustic wave filters have had a structure as shown in FIG. 13.
In a surface acoustic wave filter shown in FIG. 13, a series resonator 2 and a parallel resonator 3 which are surface acoustic wave resonators are formed on a piezoelectric substrate 1 and connected to each other to provide a filter characteristic. As the resonators, multiple pairs of interdigital transducers or an interdigital transducer with reflecting electrodes being provided on both sides have been employed.
As a document on the conventional art related to the present invention, Japanese Laid-Open Publication No. 2001-119260 is known, for example.
The structure described above has a problem that sufficient Q-factors of the resonators cannot be secured when the frequency increases. Furthermore, when a filter is formed, there is a limit on improving insertion loss and steepness.